1. Field of the Invention
This invention relates generally to a pneumatic motor actuationally utilizing the compressionally induced heat energy of a gas substantially adiabatically compressed by a compressor specialized so that compression of gas therein will approximate ideal adiabatic compression, and more specifically, this invention relates to such a motor and compressor combination wherein the motor has the form of a percussive tool, which may be a vibrationless paving breaker.
2. Description of the Prior Art
Over the preceding years, the present applicant has devoted much time and effort and has made many important inventions, some of which can be truly classified as "breakthrough" inventions, relating to the production of vibrationless pneumatic tools, such as paving breakers. (The term "vibrationless" as employed herein refers to the complete elimination of both sensible and theoretical casing vibration in a tool effectively utilizing a blow-striking element therein.) A number of these inventions have been patented, and reference may be made to the following U.S. Pat. Nos. 2,400,650, issued May 21, 1946; 2,679,826, issued June 1, 1954; 2,730,073, issued Jan. 10, 1956; 2,752,889, issued July 3, 1956; 2,985,078, issued May 23, 1961; 3,028,840, issued Apr. 10, 1962; 3,028,841, issued Apr. 10, 1962; 3,200,893, issued Aug. 17, 1965; 3,214,155, issued Oct. 26, 1965; 3,255,832, issued June 14, 1966; 3,266,581, issued Aug. 16, 1966; 3,291,425, issued Dec. 13, 1966; and 3,295,614, issued Jan. 3, 1967. Of particular interest is U.S. Pat. No. 3,200,893, in which an exhaustive discussion of the principles involved in applicant's production of vibrationless pneumatic tools is presented.
Apart from applicant's own efforts, as exemplified to some degree by the patents identified above, the vibration referenced emphasis in the field of pneumatic percussive tools has been upon reduction of vibration, in contradiction to the complete elimination of vibration sponsored by applicant in his basic approach. Accordingly, while applicant's approach results in completely vibrationless operation, the other prior art approaches have, at best, merely reduced the degree of practically occurrent vibration, which still remains at a very undesirable high level.
In prior art percussive tools, both vibrating and vibrationless, the actuating compressed gas (normally compressed air) is delivered to and utilized in the tool at a temperature in the vicinity of the ambient temperature. Therefore, there has been a very costly loss of potentially available actuating energy, due to the technologically traditional discarding of the heat energy produced in and during compression of the gas, by design deliberately directed to avoiding expansion of the compressed gas in the tool, thus rendering the system inherently inefficient.
As an informing quantitative illustration of this fact, attention is directed to the long-existing extreme contrast between the usefully transmitted mechanical-power results of actuative investments, respectively, of 100 mechanical horsepower, in an electrical generator for reclamation by and after copper wire delivery to electric motors, and in an air compressor for reclamation by and after conduit or hose delivery to pneumatic motors, the electric-motor-reclaimed mechanical power approximating 90 horsepower as against pneumatic-motor-reclaimed mechanical-power values usually in, and sometimes falling below, the range between 10 and 20 horsepower. An, because of the illustrative emphasis given herein to pneumatic motors in the particular form of hand-held pneumatic paving breakers, it is of interest to note that, in prior art pneumatic mechanical-power transmission systems consisting of compressor and hose components supplying compressed air to motor components of this particular form, the pneumatically transmitted mechanical power output resulting from such a 100-horsepower input normally does not exceed this astonishingly low 10-horsepower value, and not infrequently, in cases of field work with old and worn compressor, hose, and tool components, may decline to 8 or even to 6 horsepower.
It is not too much to say that this order-of-10 disparity between the corresponding overall efficiencies of such electric and pneumatic mechanical-power transmission systems, thus respectively approximating 90% and 10%, is the principal reason for the prior and contemporary failure of such pneumatic systems (notwithstanding their great special advantages in completely eliminating the fire and shock-hazard factors normally attending the use of the electric systems, and also in affording motor components that are uniquely superior in the respects of work-output/weight, work-output/size, and work-output/cost ratios) to generally replace such electric systems in the shop and factory market therefor which, contemporaneously and on a world sales basis, is approaching one-and-a-half billion dollars per year.
As a variant and purely qualitative expression of this very suggestive information, it is expected that the elimination of this existing order-of-10 inferiority of pneumatic mechanical-power transmission system efficiencies to electric mechanical-power transmission system efficiencies resulting from the practical equating of such pneumatic system efficiencies to such electric system efficiencies by the breakthrough achievements herein disclosed will result (inevitably, in view of the great special advantages of such pneumatic over such electric systems parenthetically recited in the preceding paragraph) in the commencement of so great an enlargement of world use of such pneumatic systems in shop and factory and in various other and actually much more extensive spheres of practical application therefor as to fully justify description of such very great enlargement of pneumatic power transmission use as constituting the innovation of a long overdue Pneumatic Age.
The foregoing remarks relevant to the employment of compressors to produce gaseous pressures for, and therefore adequate for, the practically useful actuation of pneumatic motors, illustratively and particularly in the form of pneumatic percussive tools, yet more particularly represented by vibrationless hand-held-pneumatic paving breakers, and especially relevant to and emphasizing the very low overall pneumatic efficiency of a typical system, made up of a compressor, a practically useful form of pneumatic motor, and a hose delivering actuating gas thereto at a pressure raised above ambient value by the compressor component of the system, and purposefully and successfully designed in accordance with the traditional technical ideal of avoiding expansion of the actuating gas in such motor component of the system, quite strongly suggest the desirability, at this point in explaining the background of the invention, of more particularly explaining how this traditional but mistaken ideal, principally responsible for delaying innovation of such Pneumatic Age throughout the first century of the history of the compressor and pneumatic tool industry, could ever have come to be adopted by it as its ruling principle of thermodynamic design.
In this connection it will be readily understood that, because early compressor types were heavy and only inconveniently portable between different particular working sites on any extensive project area, the use of relatively long hoses to connect easily hand-portable pneumatic tools to such inconveniently movable compressors, being the obvious alternative to frequently undergoing the inconvenience of moving the compressors, very early and widely became customary practice in project areas where compressor, hose, and pneumatic tool systems were being practically applied.
It was then found that the rate of heat transfer, through the walls of such long hoses and between compressed air flowing therein and ambient air, was generally sufficient to cause delivery of such compressed air, to the tool to be actuated thereby and regardless of its temperature of entrance into the remote other end of the hose connected to the compressor, at a temperature only unimportantly different from the temperature of the casing and interior of the tool being maintained by contact with ambient air approximately at ambient temperature. And under these conditions it was readily determined that the horsepower requirement for operating the compressor to deliver compressed air to the tool at any chosen actuating pressure and thus unavoidably at approximately ambient temperature, and at any specific pounds-per-minute rate in order to obtain a desired work-rate from the tool, could be significantly reduced by purposeful design of the compressor to reduce the disparity between the actual compression process and ideal isothermal compression at the ambient temperature.
A corollary to the general acceptance of this objective of design was a passive and continuing general acceptance of the described condition of delivery of the actuating compressed air to the tool at approximately ambient temperature, which in turn imposed the still generally accepted prohibition on design that it not permit substantial expansion of the actuating compressed air in the tool which would so reduce the temperature of such air in passing through the tool as to produce highly objectionable degrees of refrigeration therein. In recent years, one of the leading compressor and pneumatic tool manufacturers published a list of 14 impairments of tool operation which such refrigeration in the tool would usually or could sometimes produce. As examples, a not very extreme degree of refrigeration would result in liquefaction of the moisture content of the compressed air into water streaking and breaking the oil film on the internal cylinder surface of the tool, leading to rapid wear and impaired hammer-piston seal on cylinder surface areas thus deprived of effective oil lubrication, while more extreme degrees of such refrigeration could destroy all lubricative action, and therefore prevent free sliding hammer-piston motion, by solidifying the oil film, and, under certain atmospheric conditions, would stop operation of the tool entirely by converting moisture content of the compressed air into an ice plug completely blocking the exhaust port of the tool.
And this generally accepted prohibition against expansion, of the compressed air in the tool, by preventing reclamation by it of the major investment of mechanical energy in compressing air to a smaller volume in the compressor (called the energy of compression), limits the mechanical energy obtained by the tool from compressed air passing through it to the minor investment of mechanical energy made by the compressor piston (called the pumping energy) in pumping compressed air out of the compressor cylinder, without further reduction of the volume thereof, into and against the compressed air pressure effective through the receiver and/or hose.
In brief, then, the century-old commitment of the compressor and pneumatic tool industry to not reclaiming the much larger energy of compression in the tool, but instead actuatively employing in it only the much lesser pumping energy, is the principal reason for the continued survival of the hereinbefore specified, astonishingly low, overall pneumatic mechanical-power transmission efficiencies of the order of 10%.